Method and apparatus for executing conditional handover in wireless communication network

ABSTRACT

Embodiments herein disclose a method for executing conditional handover by a UE in a wireless communication network. The method may include receiving an RRC reconfiguration message from a source cell of the wireless communication network. The RRC reconfiguration message may include a handover configuration and determining whether a CHO configuration may be provided in the handover configuration. Further, the method may include performing one of: continuing an RLM timer and an RLM procedure on the source cell, in response to determining that the CHO configuration is provided in the handover configuration; and stopping the RLM timer and suspending the radio link monitoring procedure on the source cell, in response to determining that the CHO configuration is not provided in the handover configuration. The method may then include executing the CHO from the source cell to a candidate target cell in the wireless communication network based on the CHO configuration.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. § 119 of an Indian patent application number 201941012734, filed on Mar. 29, 2019, in the Indian Patent Office, and of an Indian patent application number 201941012734, filed on Mar. 25, 2020, in the Indian Patent Office, the disclosure of each of which is incorporated by reference herein in its entirety.

BACKGROUND 1. Field

The present disclosure relates to in wireless communication, and more particularly to a method and a user equipment (UE) for executing conditional handover in a wireless communication network.

2. Description of Related Art

To meet the demand for wireless data traffic having increased since deployment of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. The 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post long term evolution (LTE) system’. The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large scale antenna techniques are discussed with respect to 5G communication systems. In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation and the like. In the 5G system, hybrid frequency shift keying (FSK) and Feher's quadrature amplitude modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.

The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The Internet of everything (IoE), which is a combination of the IoT technology and the big data processing technology through connection with a cloud server, has emerged. As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “security technology” have been demanded for IoT implementation, a sensor network, a machine-to-machine (M2M) communication, machine type communication (MTC), and so forth have been recently researched. Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing information technology (IT) and various industrial applications.

In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as a sensor network, MTC, and M2M communication may be implemented by beamforming, MIMO, and array antennas. Application of a cloud RAN as the above-described big data processing technology may also be considered to be as an example of convergence between the 5G technology and the IoT technology.

As described above, various services can be provided according to the development of a wireless communication system, and thus a method for easily providing such services is required.

SUMMARY

Accordingly the embodiments herein disclose a method for executing conditional handover by UE in a wireless communication network. The method may include receiving an RRC reconfiguration message from a source cell of the wireless communication network. The RRC reconfiguration message may include a handover configuration. The method may further include determining whether a CHO configuration is provided in the handover configuration. The CHO configuration may include a plurality of conditions for performing the CHO and a plurality of target cell configurations. Further, the method may include performing one of: continuing an RLM timer and an RLM procedure on the source cell, in response to determining that the CHO configuration is provided in the handover configuration; and stopping the RLM timer and suspending the radio link monitoring procedure on the source cell, in response to determining that the CHO configuration is not provided in the handover configuration. The method may then include executing the CHO from the source cell to a candidate target cell of the plurality of target cells in the wireless communication network based on the CHO configuration.

In an embodiment, executing by the UE, the CHO from the source cell to the candidate target cell of the plurality of target cells in the wireless communication network based on the CHO configuration may include determining that the condition for executing the CHO from the source cell to the candidate target cell is fulfilled; suspending the RLM timer and the radio link monitoring procedure on the source cell; and executing the conditional handover from the source cell to the candidate target cell in the wireless communication network based on the candidate target cell configuration of the plurality of target cell configuration.

In an embodiment, the CHO configuration may include a condition for executing the CHO for the candidate target cell and a candidate target cell configuration.

In an embodiment, the plurality of target cell configurations may be carried in the RRC reconfiguration message as an OCTET string.

In an embodiment, the CHO configuration may be a delta configuration to a current source cell configuration.

In an embodiment, the plurality of target cell configurations in the CHO configuration cannot be altered by the source cell.

In an embodiment, the condition for performing the CHO may be determined and appended by the source cell to the CHO configuration.

In an embodiment, the RLM Timer may be a T310 timer.

Accordingly the embodiments herein disclose user equipment (UE) for executing conditional handover in a wireless communication network. The UE may include a transceiver, a memory, and at least one processor. The at least one processor may be configured to control the transceiver to receive an RRC reconfiguration message from a source cell of the wireless communication network, where the UE is in an RRC connected state and where the RRC reconfiguration message comprises a handover configuration. The at least one processor may be further configured to determine whether a conditional handover (CHO) configuration is provided in the handover configuration, where the CHO configuration may include a plurality of conditions for performing the CHO and a plurality of target cell configurations. Further, the at least one processor may be also configured to perform one of: continue a radio link monitoring (RLM) timer and a radio link monitoring procedure on the source cell, in response to determining that the CHO configuration is provided in the handover configuration; and stop the RLM timer and suspending the radio link monitoring procedure on the source cell, in response to determining that the CHO configuration is not provided in the handover configuration. Further, the at least one processor may be also configured to execute the CHO from the source cell to a candidate target cell of the plurality of target cells in the wireless communication network based on the CHO configuration.

Accordingly the embodiments herein disclose a method for triggering an RRC state transition indication by UE in a wireless communication network. The method includes receiving, by the UE, a radio resource control (RRC) Reconfiguration message from the wireless communication network, where the RRC Reconfiguration message comprises a configuration setting. Further, the method includes enabling, by the UE, a capability to trigger an RRC state transition indication to the wireless communication network based on the configuration setting and determining, by the UE, a condition to trigger the RRC state transition indication to the wireless communication network is satisfied. Further, the method includes triggering, by the UE, the RRC state transition indication by sending a UE assistance information message to the wireless communication network.

Accordingly the embodiments herein disclose user equipment (UE) for triggering an RRC state transition indication in a wireless communication network. The UE includes a communicator, a memory, and a processor. The communicator is configured to receive a radio resource control (RRC) Reconfiguration message from the wireless communication network, where the UE is in an RRC_CONNECTED state and where the RRC Reconfiguration message comprises a configuration setting. The processor is configured to enable a capability to trigger an RRC state transition indication to the wireless communication network based on the configuration setting. Further, the processor is also configured to determine a condition to trigger the RRC state transition indication to the wireless communication network is satisfied; and trigger the RRC state transition indication by sending a UE assistance information message to the wireless communication network.

These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

The principal object of the embodiments herein is to provide a method and a UE for executing conditional handover in a wireless communication network.

Another object of the embodiments herein is to receive an RRC reconfiguration message comprising a handover configuration from a source cell of the wireless communication network.

Another object of the embodiments herein is to determine that a CHO configuration which includes a plurality of conditions for performing the CHO and a plurality of target cell configurations is provided in the handover configuration.

Another object of the embodiments herein is to continue an RLM timer and a radio link monitoring procedure on the source cell, in response to determining that the CHO configuration is provided in the handover configuration; and stop the RLM timer and suspend the radio link monitoring procedure on the source cell, in response to determining that the CHO configuration is not provided in the handover configuration.

Another object of the embodiments herein is to execute the CHO from the source cell to a candidate target cell of the plurality of target cells in the wireless communication network based on the CHO configuration.

Another object of the embodiments herein is to suspend the RLM timer and the radio link monitoring procedure on the source cell when the condition for executing the CHO from the source cell to the candidate target cell is fulfilled.

Another object of the embodiments herein is to enable the UE to send an RRC state transition indication to the wireless communication network based on a configuration setting received in the RRC Reconfiguration message.

Another object of the embodiments herein is to determine that at least one condition to trigger the RRC state transition indication to the wireless communication network is satisfied.

Another object of the embodiments herein is to trigger the RRC state transition indication by sending a UE assistance information message to the wireless communication network.

Another object of the embodiments herein is to append a preferred RRC state of the UE in the UE assistance information message.

Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely.

Moreover, various functions described below can be implemented or supported by one or more computer programs, each of which is formed from computer readable program code and embodied in a computer readable medium. The terms “application” and “program” refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in a suitable computer readable program code. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. A “non-transitory” computer readable medium excludes wired, wireless, optical, or other communication links that transport transitory electrical or other signals. A non-transitory computer readable medium includes media where data can be permanently stored and media where data can be stored and later overwritten, such as a rewritable optical disc or an erasable memory device.

Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:

FIG. 1A illustrates a system for executing conditional handover in a wireless communication network, according to the embodiments as disclosed herein;

FIG. 1B illustrates a block diagram of a user equipment (UE) for executing the conditional handover in the wireless communication network, according to the embodiments as disclosed herein;

FIG. 2A illustrates a flow chart of a method for executing the conditional handover by the UE in the wireless communication network, according to the embodiments as disclosed herein;

FIG. 2B illustrates a flow chart of a method for triggering an RRC state transition indication by the UE in the wireless communication network, according to the embodiments as disclosed herein;

FIG. 3A illustrates a signaling diagram of a suspension of a radio link monitoring (RLM) timer immediately on receiving a handover command (HO), according to the embodiments as disclosed herein;

FIG. 3B illustrates a signaling diagram of a continuation of the RLM timer on a source cell till HO execution based on a conditional handover configuration provided in the HO command, according to the embodiments as disclosed herein;

FIG. 4 illustrates a flow chart of an RLM monitoring during the HO execution, according to the embodiments as disclosed herein;

FIG. 5A illustrates a signaling diagram of pro-active neighbor cell preparation for re-establishment, according to the embodiments as disclosed herein;

FIG. 5B illustrates a signaling diagram of target cell preparation for the HO execution, according to the embodiments as disclosed herein;

FIG. 6 illustrates a flow chart of cell selection prioritization (order) when attempting re-establishment, according to the embodiments as disclosed herein;

FIG. 7A illustrates a signaling diagram of a method of performing a UE controlled RRC_CONNECTED to RRC_INACTIVE state transition as on a configured threshold, according to the embodiments as disclosed herein;

FIG. 7B illustrates a signaling diagram of a method of performing the UE controlled RRC_CONNECTED to RRC_INACTIVE state transition as on a configured timer, according to the embodiments as disclosed herein;

FIG. 7C illustrates a signaling diagram of a method of performing the UE autonomous RRC_CONNECTED to RRC_IDLE state transition as on a configured timer, according to the embodiments as disclosed herein;

FIG. 8 illustrates a gNB according to the embodiments as disclosed herein; and

FIG. 9 illustrates a user equipment (UE) according to the embodiments as disclosed herein.

DETAILED DESCRIPTION

FIGS. 1A through 9, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system or device.

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein may be made without departing from the scope and spirit of the disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

FIG. 1 through FIG. 9, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system or device.

The term “couple” and its derivatives refer to any direct or indirect communication between two or more elements, whether or not those elements are in physical contact with one another. The terms “transmit,” “receive,” and “communicate,” as well as derivatives thereof, encompass both direct and indirect communication. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrase “associated with,” as well as derivatives thereof, means to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like. The term “processor” or “controller” means any device, system or part thereof that controls at least one operation. Such a controller may be implemented in hardware or a combination of hardware and software and/or firmware. The functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. The phrase “at least one of,” when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one item in the list may be needed. For example, “at least one of: A, B, and C” includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C.

Moreover, various functions described below can be implemented or supported by one or more computer programs, each of which is formed from computer readable program code and embodied in a computer readable medium. The terms “application” and “program” refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in a suitable computer readable program code. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. A “non-transitory” computer readable medium excludes wired, wireless, optical, or other communication links that transport transitory electrical or other signals. A non-transitory computer readable medium includes media where data can be permanently stored and media where data can be stored and later overwritten, such as a rewritable optical disc or an erasable memory device.

In view of the specification, the terms wireless communication network and network may be used interchangeably throughout the specification, and are to mean one and the same. The terms source cell and source node may be used interchangeably throughout the specification, and are to mean one and the same. The terms target cell and target node may be used interchangeably throughout the specification, and are to mean one and the same.

Definitions for other certain words and phrases are provided throughout this disclosure. Those of ordinary skill in the art should understand that in many if not most instances, such definitions apply to prior as well as future uses of such defined words and phrases.

Aspects, features, and advantages of the disclosure are readily apparent from the following detailed description, simply by illustrating a number of particular embodiments and implementations, including the best mode contemplated for carrying out the disclosure. The disclosure is also capable of other and different embodiments, and its several details can be modified in various obvious respects, all without departing from the spirit and scope of the disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. The disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings.

To meet the demand for wireless data traffic having increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a “beyond 4G network” or a “post LTE system.”

The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission coverage, the beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques and the like are discussed in 5G communication systems.

In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul communication, moving network, cooperative communication, coordinated multi-points (CoMP) transmission and reception, interference mitigation and cancellation and the like.

In the 5G system, hybrid frequency shift keying and quadrature amplitude modulation (FQAM) and sliding window superposition coding (SWSC) as an adaptive modulation and coding (AMC) technique, and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.

In general, with an increased number of users of wireless communication network, the need to provide undisrupted and high quality of service to the users is of prime importance for the telecom industry.

The wireless communication network supports communication for a plurality of user equipments (UE). Each UE communicates with one or more base stations via transmissions on forward link and reverse link. The forward link (or downlink) refers to a radio link from the base stations to the UE, and the reverse link (or uplink) refers to the radio link from the UE to the base stations. In the wireless communication network, radio link monitoring (RLM) is a mechanism for the UE to monitor quality of the downlink (DL) for determining if the radio link is good enough to continue transmission.

The base station of a source cell in which the UE is currently located, facilitates communications of the UE. Due to mobility, the UE may enter into coverage area associated with another base station which may be able to serve the UE better. However, the UE needs to perform handover procedure from the base station serving the source cell to a new base station. In conventional mobility procedures, when the UE receives a handover command, the UE suspends the radio link monitoring (i.e., RLM timer T310 is stopped). Further, the handover procedure towards a target cell is initiated immediately on reception of the handover command from the wireless communication network. An aspect of improved mobility robustness during the handover procedure is conditional Handover (CHO) which is agreed to be supported on both long term evolution (LTE) and New Radio (NR). In the CHO scenario, a candidate cell (or a potential target cell) is configured to the UE using a CHO configuration received as part of the handover command and then the CHO execution is initiated based on the UE satisfying a network configured condition. Unlike the conventional handover procedures, the UE in the CHO does not perform the handover execution immediately on receiving the handover command from the wireless communication network. Therefore, if the RLM is suspended (or if the T310 is stopped, if the T310 running), the UE may be forced to be latched on to a weak cell without being able to recover and hence become inefficient. During the CHO execution, the UE however continues to receive signals from a source cell based on a radio/RF capability. If the RLM is performed (e.g., if the T310 is not stopped, if the T310 running) during the CHO execution time, then the UE encounters a radio link failure (RLF) in the wireless communication network.

Another aspect of the UE which needs to be addressed in order to achieve higher efficiency is reduction in power consumption by the UE. The reduction in power consumption for the UE is achieved by use of mechanisms like Discontinuous Reception (DRX), over heating assistance etc. In LTE systems, the UE is configured to send power preference indication (PPI), which has a very generic purpose that the wireless communication network interprets as the UE is requesting optimized power consumption. However, a scenario of a transition of the UE from a radio resource control (RRC) CONNECTED state to one of: an RRC IDLE state or an RRC INACTIVE state is based on the discretion of the wireless communication network. There is no feedback from the UE and hence a higher possibility of increased and inefficient power consumption by the UE.

According to existing standard specifications, there is no mechanism by which the UE can indicate to the wireless communication network that radio resource control (RRC) connection can be released, thereby reducing a possible the power consumption. Even if there is no data transfer ongoing with the UE, the wireless communication network still maintains the RRC connection for duration of an inactivity timer. The inactivity timer is not defined in existing standard specification but a parameter maintained by the wireless communication network which is implementation specific. However, all wireless communication networks use the inactivity timer and do not release the RRC connection immediately in order to ensure that there are no frequent requests for the RRC connection from the UE resulting is unnecessary power consumption.

Accordingly the embodiments herein disclose a method for executing conditional handover by UE in a wireless communication network. The method may include receiving an RRC reconfiguration message from a source cell of the wireless communication network. The RRC reconfiguration message may include a handover configuration and determining whether a conditional handover (CHO) configuration is provided in the handover configuration. The CHO configuration may include a plurality of conditions for performing the CHO and a plurality of target cell configurations. Further, the method may include performing one of: continuing an RLM timer (180) and an RLM procedure on the source cell, in response to determining that the CHO configuration is provided in the handover configuration; and stopping the RLM timer and suspending the radio link monitoring procedure on the source cell, in response to determining that the CHO configuration is not provided in the handover configuration. The method may then include executing the CHO from the source cell to a candidate target cell of the plurality of target cells in the wireless communication network based on the CHO configuration

Referring now to the drawings and more particularly to FIGS. 1A through 7C, where similar reference characters denote corresponding features consistently throughout the figure, these are shown preferred embodiments.

FIG. 1A illustrates a system for executing a conditional handover (CHO) in a wireless communication network, according to the embodiments as disclosed herein.

Referring to the FIG. 1A, the system for executing the CHO in the wireless communication network may include the UE (100), a source gNB (1000 a) of a source cell within the ambit of which the UE (100) is located, a Target gNB (1000 b) of a candidate target cell and a plurality of target cells. The UE (100) may be mobile and may be in an RRC connected state with the source gNB. Due to the mobility, the UE (100) may move closer to a coverage area associated with the candidate target cell which provides better signal strength, and the UE (100) needs to execute a handover from the source gNB (1000 a) to the target gNB (1000 b). Radio link monitoring (RLM) may be a continuous procedure performed by the UE (100) to monitor quality of a downlink (DL) to continue transmission. The UE (100) may be indicated to execute the handover by sending an RRC reconfiguration message from the source cell.

Unlike to the conventional methods and systems, in the proposed method the UE (100) may not initiate the handover procedure/CHO immediately on reception of a handover command from the wireless communication network. Also, the UE (100) may not suspend the RLM procedure on the source cell (i.e., RLM timer T310 is not stopped) and hence continue to be latched to the source cell even when the handover procedure is initiated.

Therefore, the UE (100) may be not forced to be latched on to a weak cell without thereby providing better efficiency. Further, in the proposed method during the CHO execution, the UE (100) may suspend the RLM (i.e., RLM timer T310 is stopped, if the RLM timer T310 is running) during the CHO execution time which ensures that the UE (100) does not encounter a radio link failure (RLF) in the wireless communication network.

FIG. 1B illustrates a block diagram of the UE (100) for executing the CHO in the wireless communication network, according to the embodiments as disclosed herein.

Referring to the FIG. 1B, the UE (100) can be, for example, a mobile phone, a smart phone, Personal Digital Assistant (PDA), a tablet, a wearable device, or the like. In an embodiment, the UE (100) can include a communicator (120), a memory (140), a processor (160) and an RLM timer (180). The UE (100) may be in an RRC connected state.

In one embodiment, the processor (160) may include one or more processors or other processing devices that control the proposed function, process, and/or method. Operation of the UE 100 may be implemented by the processor (160).

In an embodiment, the communicator (120) may be configured to receive a Radio Resource Control (RRC) reconfiguration message from a source cell of the wireless communication network. The RRC reconfiguration message may include a handover configuration. The handover configuration may be a set of instructions used to configure parameters and settings of the UE (100) to enable the UE (100) to execute the handover from the source cell to a target cell. Further, the handover configuration may also include the target cell configuration that the UE (100) shall apply on a candidate target cell once handover procedure is successfully completed.

In another embodiment, the communicator (120) may be also configured to receive an RRC Reconfiguration message comprising a configuration setting. In the absence of the configuration setting, the UE (100) may be incapable of sending a state transition indication to the wireless communication network. The configuration setting may include information to the UE (100) that the UE (100) is allowed to send state transition request to the wireless communication network.

The memory (140) can include non-volatile storage elements. Examples of such non-volatile storage elements may include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. In addition, the memory (140) may, in some examples, be considered a non-transitory storage medium. The term “non-transitory” may indicate that the storage medium is not embodied in a carrier wave or a propagated signal. However, the term “non-transitory” should not be interpreted that the memory (140) is non-movable. In some examples, the memory (140) may be configured to store larger amounts of information than the memory. In certain examples, a non-transitory storage medium may store data that can, over time, change (e.g., in Random Access Memory (RAM) or cache).

In an embodiment, the processor (160) may include a CHO determination engine (162), an RLM management engine (164), a HO management engine (166), an RRC state transition management engine (168), a timer management engine (170) and a UE assistance info message management engine (172).

In an embodiment, the CHO determination engine (162) may be configured to determine that a conditional handover (CHO) configuration is provided in the handover configuration. The CHO configuration may include a plurality of conditions for performing the CHO and a plurality of target cell configurations associated with the plurality of target cells. The plurality of target cell configurations may be carried in the RRC reconfiguration message as an OCTET string. The CHO configuration may be a delta configuration which details changes that are required to a current source cell configuration in order to configure the target cell and execute the handover i.e., the target cell configuration is the combination of the current source configuration and the delta configuration included in the CHO configuration. However, the source cell cannot alter the plurality of target cell configurations in the CHO configuration.

In an embodiment, the RLM management engine (164) may be configured to continue a radio link monitoring (RLM) timer (180) and a radio link monitoring procedure on the source cell on determining that the CHO configuration is provided in the handover configuration. The RLM management engine (164) may be configured to stop the RLM timer (180) and suspend the radio link monitoring procedure on the source cell on determining that the CHO configuration is not provided in the handover configuration. The RLM timer (180) may be a T310 timer. Further, the RLM management engine (164) may receive an indication from the HO management engine (166) to suspend the RLM timer (180) and the radio link monitoring procedure on the source cell when the condition for executing the CHO is fulfilled, and suspend the RLM timer (180) and the radio link monitoring procedure on the source cell.

In an embodiment, the HO management engine (166) may be configured to determine the condition for executing the CHO from the source cell to a candidate target cell of the plurality of target cells and determine that the condition for executing the CHO is fulfilled. The condition for performing the CHO may be determined and appended by the source cell to the CHO configuration.

Further, the HO management engine (166) may be configured to indicate to the RLM management engine (164) to suspend the RLM timer (180) and the radio link monitoring procedure on the source cell and execute the CHO from the source cell to the candidate target cell in the wireless communication network based on the candidate target cell configuration.

In an embodiment, the RRC state transition management engine (168) may be configured to enable a capability to trigger an RRC state transition indication to the wireless communication network. The capability may be enabled by activating the condition to trigger the RRC state transition indication based on the RRC Reconfiguration message which enables the capability to send the UE assistance information for indicating RRC state transition. The condition may be one of: a timer based threshold and a counter based threshold. Further, the state transition management engine (168) may be configured to determine that at least one condition to trigger the RRC state transition indication to the wireless communication network is satisfied. The activated condition based on the timer threshold may be one of: determining that the UE (100) is explicitly configured with a dataInactivityTimer; configuring an inactiveIndicationTimer when the UE (100) is not explicitly configured with the dataInactivityTimer; and determining that a threshold condition as a percentage of time for one of: the dataInactivityTimer and the inactiveIndicationTimer is met when said timer is running. The activated condition based on the counter threshold may include determining a drxInactivityTimer is not started at least once on activating the trigger condition and a configured number of DRX cycles is elapsed without one of transmission or reception between the UE (100) and the wireless communication network, wherein the drxInactivityTimer is part of an RRC_CONNECTED state DRX cycle configuration.

The configuring of the inactiveIndicationTimer when the UE (100) is not explicitly configured with the dataInactivityTimer may include determining that the UE (100) is not explicitly configured with the dataInactivityTimer by the wireless communication network and configuring, by the UE (100), the UE (100) with the inactiveIndicationTimer. A condition to one of: start the inactiveIndicationTimer and re-start the inactiveIndicationTimer may be same as the condition to one of: start the dataInactivityTimer and re-start the dataInactivityTimer.

Further, the state transition management engine (168) may be configured to switch to one of: an RRC IDLE and an RRC INACTIVE state from the RRC_CONNECTED state based on an RRL release message received from the wireless communication network.

In an embodiment, the UE assistance info message management engine (170) may be configured to determine whether a preferred RRC state of the UE (100) to switch from the RRC_CONNECTED state is available. Further, on determining that the preferred RRC state of the UE (100) to switch from the RRC_CONNECTED state is available, the UE assistance info message management engine (170) may be configured to append the preferred RRC state of the UE (100) in the UE assistance information message which is then sent to the wireless communication network. When the preferred RRC state of the UE (100) is indicated in the UE assistance information, the preferred RRC state of transition may be RRC INACTIVE state. On determining that the preferred RRC state of the UE (100) to switch from the RRC_CONNECTED state is unavailable, the UE assistance info message management engine (170) may be configured to send the UE assistance information message to the wireless communication network without the preferred RRC state of the UE (100). When the preferred RRC state of the UE (100) is not indicated in the UE assistance information, the state transition may indicate one of: the RRC INACTIVE state and an RRC IDLE state. The UE assistance information may be an indication to the wireless communication network to trigger the state transition from the RRC CONNECTED state.

Although the FIG. 1B shows the hardware elements of the UE (100) but it is to be understood that other embodiments are not limited thereon. In other embodiments, the UE (100) may include less or more number of elements. Further, the labels or names of the elements are used only for illustrative purpose and does not limit the scope of the disclosure. One or more components can be combined together to perform same or substantially similar function.

FIG. 2A illustrates a flow chart 200 a of a method for executing the CHO by the UE in the wireless communication network, according to the embodiments as disclosed herein.

Referring to the FIG. 2A, at step 202 a, the UE may receive the RRC reconfiguration message from the source cell of the wireless communication network. For example, in the UE (100) as illustrated in the FIG. 1B, the communicator (120) can be configured to receive the RRC reconfiguration message from the source cell of the wireless communication network.

At step 204 a, the UE may determine whether the conditional handover (CHO) configuration is provided in the handover configuration. For example, in the UE (100) as illustrated in the FIG. 1B, the processor (160) can be configured to determine that the conditional handover (CHO) configuration is provided in the handover configuration.

At step 206 a, the UE may continue the radio link monitoring (RLM) timer and the radio link monitoring procedure on the source cell, in response to determining that the CHO configuration is provided in the handover configuration. For example, in the UE (100) as illustrated in the FIG. 1B, the processor (160) can be configured to continue the radio link monitoring (RLM) timer and the radio link monitoring procedure on the source cell, in response to determining that the CHO configuration is provided in the handover configuration.

At step 208 a, the UE may stop the radio link monitoring (RLM) timer and suspend the radio link monitoring procedure on the source cell, in response to determining that the CHO configuration is not provided in the handover configuration. For example, in the UE (100) as illustrated in the FIG. 1B, the processor (160) can be configured to stop the radio link monitoring (RLM) timer (180) and suspend the radio link monitoring procedure on the source cell, in response to determining that the CHO configuration is not provided in the handover configuration.

At step 210 a, the UE may determine that the condition for executing the CHO from the source cell to the candidate target cell is fulfilled. For example, in the UE (100) as illustrated in the FIG. 1B, the processor (160) can be configured to determine that the condition for executing the CHO from the source cell to the candidate target cell is fulfilled.

At step 212 a, the UE may suspend the RLM timer (180) and the radio link monitoring procedure on the source cell. For example, in the UE (100) as illustrated in the FIG. 1B, the processor (160) can be configured to suspend the RLM timer (180) and the radio link monitoring procedure on the source cell.

At step 214 a, the UE may execute the CHO from the source cell to the candidate target cell in the wireless communication network based on the candidate target cell configuration of the plurality of target cell configuration. For example, in the UE (100) as illustrated in the FIG. 1B, the processor (160) can be configured to execute the CHO from the source cell to the candidate target cell in the wireless communication network based on the candidate target cell configuration of the plurality of target cell configuration.

The various actions, acts, blocks, steps, or the like in the method may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some of the actions, acts, blocks, steps, or the like may be omitted, added, modified, skipped, or the like without departing from the scope of the invention.

FIG. 2B illustrates a flow chart 200 b of a method for triggering an RRC state transition indication by the UE (100) in the wireless communication network, according to the embodiments as disclosed herein.

Referring to the FIG. 2B, at step 202 b, the UE may receive the radio resource control (RRC) Reconfiguration message from the wireless communication network. For example, the UE (100) as illustrated in the FIG. 1B the communicator (120) is configured to receive the radio resource control (RRC) Reconfiguration message from the wireless communication network.

At step 204 b, the UE may enable to send the RRC state transition indication to the wireless communication network based on the configuration setting received in the RRC Reconfiguration message. For example, the UE (100) as illustrated in the FIG. 1B the processor (160) is configured to enable the UE (100) to send the RRC state transition indication to the wireless communication network based on the configuration setting received in the RRC Reconfiguration message.

At step 206 b, the UE may determine that at least one condition to trigger the RRC state transition indication to the wireless communication network is satisfied. For example, the UE (100) as illustrated in the FIG. 1B the processor (160) is configured to determine that at least one condition to trigger the RRC state transition indication to the wireless communication network is satisfied.

At step 208 b, the UE may determine whether the preferred RRC state of the UE (100) to switch from the RRC_CONNECTED state is available. For example, the UE (100) as illustrated in the FIG. 1B the processor (160) is configured to determine whether the preferred RRC state of the UE (100) to switch from the RRC_CONNECTED state is available.

At step 210 b, in response to determining that the preferred RRC state of the UE to switch from the RRC_CONNECTED state is available, the UE may append the preferred RRC state of the UE in the UE assistance information message. For example, the UE (100) as illustrated in the FIG. 1B the processor (160) is configured to append the preferred RRC state of the UE (100) in the UE assistance information message.

At step 212 b, the UE may trigger the RRC state transition indication by sending the UE assistance information message to the wireless communication network. For example, the UE (100) as illustrated in the FIG. 1B the processor (160) is configured to trigger the RRC state transition indication by sending the UE assistance information message to the wireless communication network.

At step 208 b, in response to determining that the preferred RRC state of the UE to switch from the RRC_CONNECTED state is not available, the UE may loop to step 212 b.

The various actions, acts, blocks, steps, or the like in the method may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some of the actions, acts, blocks, steps, or the like may be omitted, added, modified, skipped, or the like without departing from the scope of the invention.

FIG. 3A illustrates a signaling diagram of a suspension of the RLM timer (180) by the UE (100) immediately on receiving the handover (HO) command, according to the embodiments as disclosed herein.

Referring to the FIG. 3A, at step 302 a, consider that the UE (100) is in the RRC connected state with the source gNB (1000 a). In the RRC connected state, at step 304 a, the source gNB (1000 a) sends a measurement configuration to the UE (100). Further, at step 306 a, the UE (100) sends measurement report to the source gNB (1000 a). The measurement report includes a current configuration associated with the UE (100). The UE (100) performs the RLM by estimating the downlink radio link quality and compare the downlink radio link quality to preset thresholds Qout for monitoring the downlink radio link quality of the source cell (Pscell) to detect a radio link failure (RLF). The preset threshold Qout is defined as a level at which the downlink radio link cannot be reliably received and shall correspond to the out-of-sync block error rate (BLERout).

Further, the UE (100) measures a Block Error Rate (BLER) of a Physical Downlink Control Channel (PDCCH) during a predetermined time period. Further, at step 308 a, the UE (100) determines that the BLER drops below the preset threshold (Qout) during the predetermined time period and an out-of-sync indication is generated in a physical (PHY) layer. When a preset N310 number of successive out-of-sync indications are reported to the RRC layer by the PHY layer, the RLM timer (180) is started by the RRC layer (step 310 a).

At step 312 a, the source gNB (1000 a) sends the RRCReconfiguration message to the UE (100). In the conventional methods and systems, the UE (100) in response to receiving the RRCReconfiguration message, at step 314 a, stops the RLM timer (180) on and at step 316 a, suspends the RLM procedure. Further, at step 318 a, the UE (100) executes the handover from the source cell to the target cell and at step 320 a, sends the Reconfiguration complete message to the target gNB (1000 b).

However, the signaling in the CHO scenario may be similar to signaling in the HO scenario with some changes. The HO signaling for the CHO scenario may include some limitations such as:

-   -   1) Whether to support candidate target cells controlled by         different target nodes (which may affect radio signaling)     -   2) Whether to support candidate target cells on different         carrier frequencies/MOs (which may affect the CHO configuration         to be provided for the candidate)     -   3) Whether same handover configuration parameters can be         signaled by the target node at the CHO preparation. Further, the         CHO configuration may include only the most essential parameters         which need to be updated in the source cell configuration.

In order to achieve the CHO, the configuration parameters are typically configured by the source node (source cell) and the target node (target cell) at the CHO configuration (i.e., in signaling towards the UE (100)) and are assumed to be known. Further,

-   -   1) the source node controls the CHO candidates which are to be         configured and therefore, the source node sets:         -   a) the CHO condition i.e., something based on A3 or A5             (possibly only need to indicate offset as based on the             condition for measurement used to add the CHO candidate)         -   b) the validity timer i.e., a timer upon the expiry of which             the UE (100) releases the CHO configuration (i.e., the             source node manages the plurality of the CHO candidates but             may not always succeed in releasing the at least one CHO             candidate of the plurality of CHO candidates)         -   c) Further, the UE (100) should be allowed to set a             different value for each of the CHO candidate, at least for             the CHO condition.     -   2) The target node sets the configuration to be used when the UE         (100) moves to the CHO from an initial access. However, some of         the important considerations with respect to the configuration         by the target node include:         -   A. reconfigurationWithSync is the most essential             configuration parameter and particularly:             -   a) contention-free based random access (CFRA) resources                 (e.g. for all wide/cell specific beams, given delay                 between the CHO configuration and execution)             -   b) PCell (dedicated and common) configuration             -   c) T304 (to guard the actual CHO execution phase i.e.,                 started after the CHO condition is achieved)         -   B. the network can include other configuration such as for             example: radioBearerConfig, RLC bearerConfig, MAC config,             measConfig. However, to avoid the need to reconfigure, the             network may only include the most essential parameters in             the CHO configuration. The configuration which may not be             essential are temporarily suspended/deactivated and then             resumed/re-activated upon the first subsequent             reconfiguration (i.e., when the network can modify)             -   a) measConfig may need to be changed i.e., to continue                 measurements on the new primary frequency (for the case                 of inter-frequency CHO)             -   b) If multiple CHO candidates are configured, then the                 other configuration may not be the same for all the                 candidates i.e., for example, when the candidates are on                 different frequencies (different measConfig) or                 controlled by the different target nodes (with different                 capabilities/typical settings).         -   C. The CHO configuration is assumed to be the delta             configuration compared to the current source configuration             (i.e., source config as used at the time of the CHO             configuration).

Further, after initiating the CHO configuration, the source node should be able to modify the source configuration as:

-   -   I. Some reconfiguration cannot be postponed. Such as for example         addition of a QoS flow or DRB upon activation of a service with         specific QoS requirements     -   II. Some of the source reconfigurations affect the configuration         to be used after the execution of the CHO such as for example if         new QoS flows or DRBs are added, they should continue after the         CHO configuration i.e., affect the CHO configuration.         Therefore, the specification changes for the CHO may be limited         in the existing methods and systems.

In the proposed method, the basic starting points for performing the conditional handover may be as follows:

-   -   a) the source node (at least) sets the CHO condition and the         source node should be able to configure different values for the         different candidates.     -   b) determine whether the CHO target cell configuration should         cover parameters other than the reconfigurationWithSync for         example parameters such as:     -   measConfig, radioBearerConfig and/, L2 config or not cell         specific L1 config. Further, in case the CHO target cell         configuration should cover the parameters, then determine         whether the target node should be able to set different values         for the configuration parts for the different CHO candidates.

The method for signaling of the configuration changes when the source reconfiguration affects the CHO configuration may require that the source node should be able to modify the source configuration after having initiated the CHO configuration and in some cases the configuration to be used in the CHO candidate after the CHO execution is affected.

Consider a scenario where the source node initiates the configuration change that should continue after the CHO execution i.e., for example addition of a QoS flow or DRB. As indicated previously, we assume the CHO configuration is indicated by signaling the delta compared to the current source configuration (i.e., at the time of the CHO configuration). B. To ensure the change of the source cell configuration continues after the CHO execution, the source node could either indicate the target cell of the CHO by signaling:

-   -   a) Delta compared to the updated source cell configuration     -   b) Delta compared to the previous CHO configuration option a) is         the simplest, as the source cell configuration is same as used         at the initial CHO configuration.

Further, another issue is whether the change to the source cell configuration and the target cell configuration should be signaled together (i.e., in the same message), or can the signaling be done separately (i.e., in different messages):

-   -   1) When signaling the changes to the source cell configuration         and the target cell configuration together:         -   a) The changes will succeed/fail jointly (+)         -   b) Will require some means to distinguish which             configuration part concerns with the source CHO             configuration and which part concerns with the target CHO             configuration     -   2) When signaling the changes to the source cell configuration         and the target cell configuration separately:         -   a) There may be collision problems i.e., the UE (100)             executes the CHO in-between the two messages. This may apply             even if the two messages are transmitted together (as             processing is done sequentially)

In an embodiment of the proposed method, the CHO configuration may be indicated by signaling the delta compared to the current source configuration i.e., both at the initial setup and upon reconfiguration of the CHO configuration.

In another embodiment, the conditional handover may support simultaneous reconfiguration of the source cell and the CHO configuration i.e., together within the same message.

Further, another issue is about how to signal the source cell configuration and the target cell configuration parts i.e., for example using a container/field. Conventionally, both the source cell and the target cell generate some configuration parameters that are to be provided to the UE (100). There are different ways to signal the configuration parameters to the UE (100) such as:

-   A. A regular reconfiguration message may be used, including the     parameters generated by the source node and by the target node;     i.e., either     -   A1: The source node may forward the parameters generated by the         source node to the target node, which generates the Uu message         including these source controlled parameters     -   A2: The source node may decode the message generated by the         target and adds the parameters -   B. A container may be added to the reconfiguration message i.e., to     carry the configuration generated by the target node (alike in case     of Inter Radio Access Technology handover (IRAT HO))     -   B.1: Octet string/container may carry the Reconfiguration         message     -   B.2: Octet string/container may carry an IE including a subset         of the fields of the Reconfiguration message.

Further, when the container is added to the reconfiguration message, the support to signal the change of the source cell configuration and the CHO candidate configuration together is easier. Moreover, the fields which concern the CHO configuration are clearly defined. However, when the regular reconfiguration message is used to signal the configuration parameters to the UE (100), the procedure is not straightforward. For example, there may be a need to introduce specific fields for the CHO candidate configuration e.g. a separate spCellConfig, measConfig. Further, the usage of the regular reconfiguration message may require specifying of the fields that the target cell can set/change as part of the CHO configuration i.e., it limits network implementation.

The option B.1 is preferable and avoids the need to discuss details about which fields can be set as part of the CHO configuration and hence in the proposed method the octet string/container is added to the reconfiguration message to carry the CHO configuration generated by the target node (alike in case of IRAT HO). This octet string carries a Reconfiguration message.

Furthermore, another issue is about signaling the target configuration for multiple CHO candidates for example sending individual message per candidate. Also, the issues of how to signal the CHO configuration when there are multiple CHO candidates. The available techniques include signaling using:

I: A single message

II: A message per CHO candidate

When the single message is used to signal the CHO configuration to the multiple CHO candidates, the option to include multiple spCells/reconfigurationWithSync fields needs to be added. The same applies for other fields which value may differ per CHO candidate.

The usage of separate message per CHO candidate to signal the CHO configuration to the multiple CHO candidates, may provide a more flexible signaling structure:

-   -   1) The specification changes will be limited to introducing         multiple octet string containers.     -   2) This option can support the CHO candidates on different         target nodes     -   3) The signaling is future proof

Further, the issue relates to the outcome of the RAN2 being requested to review and confirm the general starting points. The issue also relates to adding the octet string/container to the reconfiguration message to carry the CHO configuration that touches the same aspect of whether or not the signaling should be flexible or restrictive.

In another embodiment of the proposed method, a list of octet string/containers may be added to the reconfiguration message, where each of the octet string/container is carrying the CHO configuration of a single CHO candidate as generated by the target node (alike in case of IRAT HO). Each octet string may carry a Reconfiguration message.

The usage of separate message per CHO candidate to signal the CHO configuration to the multiple CHO candidates may result in duplicate transfer of other configuration that is same for multiple candidates. However, the duplication of the configuration may be avoided for example by an indication that the value is same as of another entry in the list.

According to the earlier embodiment, source (at least) may set the CHO condition and signal the CHO condition per candidate. There may be 2 different ways to provide the CHO condition per candidate:

-   -   II.1: The source node includes a CHO candidate list field, for         these source controlled parameters (e.g. condition)     -   II.2: The source node forwards the parameter to the target node,         which includes the CHO condition in the target generated message         (for each candidate)

Option II.1 may be somewhat more in the spirit of the proposed method. On the other hand, from the UE (100) perspective it may be simplest to not have a separate CHO candidate list field to be associated with a target generated container. Hence preference may be for option II.2

Therefore, in an embodiment of the proposed method, the source node may forward the CHO candidate parameters that it controls to the target node, and the target node may include it in the target generated message (per each candidate).

Another issue which needs to be addressed is about when to send the CHO complete message by the UE.

The techniques available may include:

-   -   1. Upon the CHO execution i.e., following initial access in the         candidate cell (as done for the regular HO scenario), and     -   2. Immediately i.e., upon the CHO configuration (in which case         some other signal may be needed to be sent upon the CHO         execution).

In order to select the technique for sending the CHO complete message by the UE (100), the concerns about the action required upon the CHO configuration including the case in which the UE (100) is unable to comply with the CHO configuration needs to be addressed. Further, the assumption is that the UE (100) performs re-establishment, but the UE (100) may perform the action either upon the CHO configuration or upon the CHO execution. Also, there may be no real benefit in delaying re-establishment until the CHO execution. If however the UE (100) is able to comply, there seems no real need for an RRC message to confirm receipt and proper comprehension (i.e., L2 ACK seems sufficient); i.e., option 1, that is aligned with the regular HO seems sufficient.

Consider a scenario when the reconfiguration message also includes the change of the source cell configuration. Then, the UE may return the complete message to confirm the source cell reconfiguration. There however seems no need to include any indication regarding the CHO reconfiguration.

In an embodiment, the UE may return a CHO complete message upon the execution of the CHO i.e., following initial access in the candidate cell (as for regular HO). If the message including the CHO configuration also includes a source cell reconfiguration, the UE may immediately return a complete message (without explicit confirmation of receipt/comprehension of the CHO reconfiguration). In case of non-comprehension of the CHO configuration, the UE may immediately perform re-establishment (i.e., not delayed until the CHO execution).

In the conventional radio link monitoring procedure performed during mobility, currently available in the LTE and the NR, the RLM may be suspended (RLM timer (180) T310 is stopped, if the T310 is running) immediately on reception of the HO command from the network. The HO procedure may be performed when the signal quality of the source cell becomes weak and the signal quality of a neighbouring cell become stronger thereby making the neighbour cell better suited to serve the UE. As a result, the HO command may be normally signalled to the UE when the signal condition of the source cell is weak. Additionally, there is good probability that the UE fails to perform handover due to the inability to successfully receive the HO command from the network due to deterioration of the serving cell signal conditions. In order to reduce handover failures caused due to the failure in receiving the HO command, early handover provisioning using CHO mechanisms are also being discussed in RAN2. Further, the HO command may be signalled to the UE (100) when the serving cell signal condition is weak and there is a possibility of the HO failure due to the inability to receive the message successfully.

Consider that the UE (100) is configured with enhanced make before break (eMBB) handover then the UE (100) is expected to synchronize to the target cell and initiate random access procedure while the connection to the source cell is still active, although the signal condition may still be weak. There may be two distinct possibilities of the handover failure i.e., the source cell may encounter RLF or the target cell may encounter handover failure. However, the handover command may be provided to the UE (100) when the serving cell signal conditions are detected to be getting weaker and that the neighbour cell (target cell for handover) has a better signal conditions and thereby more suitable to serve the UE (100). Therefore, the probability of encountering the radio link failure on the source cell may be higher as compared to that of handover failure on the target cell. Further, the probability of encountering the radio link failure on the source cell may be higher as compared to that of handover failure on the target cell in the eMBB handover.

Therefore, if the UE (100) continues to perform radio link monitoring on the source cell during HO execution period, it is possible that the UE (100) declares the RLF on the source cell due to which the UE (100) has to abort the HO execution on the target cell and will result in the UE (100) performing the re-establishment procedure. The premature suspension of the HO execution can be avoided if the UE (100) does not initiate the re-establishment procedure if the radio link failure is detected on the source cell while the handover execution on the target cell is still in progress, thereby allowing the UE (100) to continue with the handover execution on the target cell without any interruption. Alternately, the radio link monitoring on the source cell can be suspended the when handover command is received. However, both the methods may be performed to achieve a similar objective and one does not appear to be better than the other.

Unlike to the conventional methods and systems, in the proposed method the radio link monitoring is suspended on reception of the HO command as the same is in-line with behaviour defined in specification for existing mobility mechanisms. Further, the result of suspending the radio link monitoring on the source cell on reception of the HO command from the network is similar to that of the UE (100) not initiating the re-establishment when the RLF is declared on the source cell while the HO execution to the target cell is in progress.

In an embodiment, the UE (100) may suspend the radio link monitoring on the source cell on receiving the HO command which includes the make before break indication. The above described UE (100) behaviour is illustrated in the FIG. 1. This can further be applied to any handover type wherein the UE (100) executes immediate handover upon reception of the HO command from the network.

Consider the scenario when the UE (100) is configured with the conditional handover (CHO). In case of the CHO mechanism, the HO command may be expected to be received much earlier than the intended time of the actual execution of the handover. The HO command may be sent in advance in case of the CHO to avoid handover failure due to the UE (100) not receiving the handover command successfully. In such cases the suspension of the radio link monitoring on the reception of the HO command from the network may not be right. Therefore, the UE (100) may continue the radio link monitoring on the source cell when the CHO is configured to the UE (100). When the handover is being executed by the UE (100) on the target cell upon meeting the condition defined in the HO command, then the UE (100) should suspend the radio link monitoring on the source cell i.e., stop T310 (if running). If the RLM is continued when UE (100) initiates the handover execution on the target cell there is a risk of facing the RLF on the source cell resulting in the premature failure of the handover to the target cell. Therefore, the radio link monitoring on the source cell should be suspended when the handover execution is initiated upon the condition defined in the HO command is met.

In an embodiment, when the UE (100) is configured with the conditional handover (CHO), the radio link monitoring on the source cell may be continued when the handover command is received from the network. In another embodiment, when the UE (100) is configured with the conditional handover (CHO), the radio link monitoring on the source cell may be suspended when the UE (100) initiates the handover execution to the target cell when the condition configured in the handover command is met. In an embodiment, the UE (100) may support one of the LTE RAT and the NR RAT.

FIG. 3B illustrates a signaling diagram of the continuation of the RLM timer (180) on the source cell till the execution of the HO command based on the CHO configuration, according to the embodiments as disclosed herein.

Referring to the FIG. 3B in conjunction with the FIG. 3A, the steps 302 b to 312 b in the FIG. 3B may be substantially the same as steps 302 a to 312 a in the FIG. 3A, and, thus repeated description is omitted. At step 314 b, unlike to the conventional methods and systems, the UE (100) may continue the T310 timer on receiving the HO command and may also at step 316 b continue the RLM procedure on the source cell. Further, at step 318 b, the UE (100) may monitor for satisfying the condition provided in the HO command for performing the conditional handover. At step 320 b, in response to determining that the condition for performing the conditional handover is satisfied, the UE (100) may suspend the RLM (stop T310 if running) on the source cell when the HO execution procedure is initiated. Further, at step 322 b, the HO execution procedure may be completed and at step 324 b, the UE (100) may send the Reconfiguration complete message to the target gNB (1000 b).

When the UE (100) is configured with the enhanced make before break (eMBB) and the conditional handover (CHO) for the same target cell, then the MBB/eMBB configuration may be provided in addition to the CHO criteria in the HO command. In such HO type, since the HO execution criteria are included, the HO command may be received earlier in time than the need to perform the HO execution. During this time, the serving cell condition may be expected to be sufficient to serve the UE (100) and the neighbour cells may not be suitable to handle the UE (100) under current signal conditions. If the radio link monitoring for the source cell is suspended in such cases, then the UE (100) may get locked on to the serving cell without having a mechanism to recover from the link degradation and related issues when the UE (100) moves towards a cell edge or out of coverage of the serving cell. Therefore, if the make before break (MBB/eMBB) handover in combination with the CHO is indicated, the UE (100) may need to continue the RLM procedure on the serving cell when the HO command is received.

However, the HO execution may be initiated by the UE (100) only when the CHO condition is met where the UE (100) follows the MBB/eMBB configuration provided in the HO command. When the CHO condition is met, then the serving cell signal conditions may start degrading and the neighbour cell may become better suited to serve the UE (100) further. In such cases, the probability of the radio link failure on the source cell may be expected to be higher than the probability of the HO failure on the target cell as the target cell has satisfied the condition required for performing the HO.

In an embodiment, the UE (100) configured with a HO type that combines make before break handover configuration and the CHO condition, the UE (100) suspends the radio link monitoring on the source cell when the HO execution to the target cell is initiated in the event when the condition configured in the HO command is met.

In another embodiment, when the UE (100) is configured with a HO type that combines make before break configuration and the CHO condition, the radio link monitoring on the source cell may be continued by the UE (100) upon reception of the HO command from the network.

In yet another embodiment, when the UE (100) is configured with a HO type that combines the enhanced make before break handover configuration and the CHO condition, the radio link monitoring on the source cell may be continued by the UE (100) upon reception of the HO command from the network.

In yet another embodiment, when the UE (100) is configured with a HO type that combines the enhanced make before break configuration and the CHO condition, the radio link monitoring on the source cell may be suspended by the UE (100) when the HO execution to the target cell is initiated in the event when the condition configured in the HO command is met. Thus the UE (100) behaviour is illustrated in the FIG. 3B.

Therefore, unlike to the conventional methods and systems, in the proposed method, whenever the condition for performing the CHO is provided, or whenever a condition is specified along with any HO command, the RLM monitoring on the source cell is continued even after the HO command is received from the network. The RLM on the source cell is suspended only once the HO execution to the target cell is initiated (when the condition in the HO command is satisfied for the UE (100)).

FIG. 4 illustrates a flow chart 400 of the radio link monitoring during the HO execution, according to the embodiments as disclosed herein.

In an embodiment, consider the RLM monitoring for a NR UE which is controlled as described in the FIG. 4. The UE may be the NR UE. At step 402, when the NR UE is in the RRC CONN state, the MR (Measurement Report) may be sent to the source cell and at step 404, the RRC CONN state procedure may be performed. Further at step 406, the NR UE may determine whether the HO command is received from the network. In response to determining that the HO command is not received at the step 406, the NR UE may loop back to the step 404. In response to determining that the HO command is not received at the step 406, the NR UE at step 408 may determine whether the HO command includes the CHO configuration.

In response to determining that the HO command includes the HO type indicated in the Rel 15 HO or Rel 16 MBB/eMBB HO, at step 418, the NR UE may stop the RLM timer (180) i.e., the T310 timer immediately on reception of the HO command and suspends the RLM on the source cell.

In response to determining that the HO command includes the HO type indicated as one of: the conditional handover criteria, or a combination of the Rel 15 HO or the Rel 16 MBB/eMBB HO and the conditional handover criteria, then the NR UE at step 410, may continue the RLM timer (if the T310 timer is already running) and continues the RLM procedures on the source cell.

Further at step 412, the NR UE may determine whether the conditional handover criteria is satisfied. In response to determining that the conditional handover criteria is not satisfied, the NR UE may loop to the step 410. In response to determining that the conditional handover criteria is satisfied, the NR UE may initiate the HO execution at step 414 and also suspend the RLM for the source cell (i.e., the T310 timer is stopped, if the T310 timer running). Further, at step 416, the NR UE may execute the handover and switches from the source cell to the candidate target cell.

In an embodiment, the UE may be the LTE UE. At step 408, when the HO type indicated to the LTE UE is Rel 16 eMBB HO or any pre-Rel16 HO, then at step 422, the UE shall, stop the T310 immediately on reception of HO command (suspend RLM on source cell).

At step 408, when the HO type indicated to the LTE UE is one of: conditional handover criteria and a combination of the Rel 16 eMBB or any of the pre-Rel16 HO and the conditional handover criteria, then at step 410, the UE shall continue the T310 timer (if the T310 timer is running) and the RLM procedures on the source cell. Further, when the HO execution begins in the event conditional handover criteria are met (at step 412), the UE may suspend the RLM for the source cell (T310 timer stopped if the T310 timer running) (as indicted in the step 414).

FIG. 5A illustrates a signaling diagram of pro-active neighbour cell preparation for re-establishment to perform handover failure recovery, according to the embodiments as disclosed herein.

FIG. 5B illustrates a signaling diagram of target cell preparation for the HO execution, according to the embodiments as disclosed herein.

Consider a scenario where the UE (100) encounters the radio link failure (RLF). In response to the RLF, the UE (100) may perform the cell selection procedure in order to select a suitable cell to re-establish the connection with the network. If the suitable cell is selected while the timer T311 is still running, then the UE (100) may attempt to re-establish the RRC connection, otherwise the UE (100) may transit to an idle state. Further, the UE (100) may decide the target cell for the re-establishment based on the cell search order and the cell signal quality.

The latency produced in the phase of handover failure recovery can be reduced by the network, by assisting the UE (100) with the preparation of the cell(s) on which the UE (100) can perform the re-establishment. However, the assistance information may become useful only if the source cell (on which the RLF is being triggered) has already prepared the potential target cell (on which the UE (100) can perform the re-establishment) with the UE (100) context prior to the UE (100) encountering the RLF. Therefore, the UE (100) may inform the network in advance via the measurement report about the presence of a certain neighbour cells which in turn allows the network to proactively prepare the neighbour cell to accommodate for the potential re-establishment from the UE (100). The preparation of the target cells for the re-establishment may include: at step 502 a, the UE (100) may receive the measurement configuration from the source gNB (1000 a). At step 504 a, the UE (100) may send the measurement report to the source gNB (1000 a). Further, the source gNB (1000 a) may communicate with the target gNB (1000 b) and prepare the target cell for performing the re-establishment. Further, the target gNB (1000 b) may send the RRC Reconfiguration with the list of target cells which can be used for re-establishment.

The sequence of procedures and the signalling involved in order to support early preparation of the target cells for the re-establishment are similar to that of the handover signalling (as described in steps 502 b-508 b except for the step 506 b where the source gNB (1000 a) prepares the target cell for performing the handover). Therefore, the network need not assist the UE (100) with the list of prepared cells. Instead, the network may rather choose to perform the handover.

FIG. 6 illustrates a flow chart 600 of the cell selection prioritization (order) when the UE (100) attempts the re-establishment of the connection with the wireless communication network, according to the embodiments as disclosed herein.

In another embodiment, the target cell may be selected for handover failure recovery, for example, by prioritizing the cells for which the measurement report is sent to the source cell. On receiving the measurement report from the UE, the source cell may have prepared the target cells with the UE context. The UE may leverage that the source cell has prepared the target cells with the UE context and attempt for the failure recovery on the target cells. Further, when the UE selects a suitable cell for performing the re-establishment of the RRC connection, if the T311 is still running on the UE, then the UE may initiate the random access procedure and the T301 may be stared. The T301 may be used in order to monitor and control the success/failure of the random access procedure and hence cannot be optimized.

Simultaneously, the target cell may try to fetch the UE context from the source cell after the successful reception of the re-establishment request from the UE. The reduction in the UE context retrieval time is possible if the UE (100) attempts the re-establishment on the cells for which the measurement report is sent to the source cell. On receiving the measurement report from the UE (100), the source cell may have successfully prepared the target cell prior to the UE (100) encountering the radio link failure. The scenario can be handled if the UE (100) follows the prioritized cell selection procedure.

In the prioritized cell selection procedure, during the handover failure or the radio link failure recovery procedure, a higher priority is provided for the cell for which a measurement report is sent to the source cell prior to the RLF. Therefore, the UE (100) may attempt to re-establish the connection to the cells which may already be prepared for the UE based on the measurement report which is previously sent to the source cell. Further, the next higher priority may be given to the cells that were detected when on the source cell but for which the measurement report is not triggered. The re-establishment may be attempted for the next higher priority cells as there is a high probability that the UE is still in vicinity of the detected cells while attempting to perform the re-establishment. Further, the next priority may be provided to all the remaining other cell.

Sequence of procedures involved in selecting target cell for handover failure or radio link failure recovery is illustrated in the FIG. 6. At step 602, the UE which is in the RRC CONN state, may perform the RLM procedure. At step 604, the UE may determine whether the RLF is declared. In response to determining that the RLF is not declared, the UE may continue the RLM procedure. In response to determining that the RLF is declared, at step 606, the UE may determine whether the measurement report is sent on the source cell.

On determining that the measurement report is sent on the source cell, at step 608, the UE may attempt the target cell selection on the target cells for which the MR was sent. Further, at step 610, the UE may determine whether a suitable target cell (candidate target cell) is found to which the UE can perform the re-establishment. In response to determining that the suitable target cell is found, at step 620, the UE may select the target cell and performs the re-establishment procedure.

In response to determining that the suitable target cell is not found, at step 612, the UE may attempt the target cell selection on the target cells that were detected and measured in the RRC CONN state. Further, at step 614 a, the UE may determine again whether the suitable target cell is found to which the UE can perform the re-establishment. In response to determining that the suitable target cell is not found, at step 616, the UE may attempt target cell selection on other target cells and may then again check whether the suitable target cell is found at step 618. At step 614 and step 618, in response to determining that the suitable target cell is found, the UE may select the target cell and performs the re-establishment procedure (step 620).

FIG. 7A illustrates a signalling diagram of a method of performing the UE controlled state transition from RRC_CONNECTED state to RRC_INACTIVE state as on a configured threshold, according to the embodiments as disclosed herein.

FIG. 7B illustrates a signalling diagram of a method of performing the UE controlled state transition from the RRC_CONNECTED state to the RRC_INACTIVE state transition as on a configured timer, according to the embodiments as disclosed herein.

FIG. 7C illustrates a signalling diagram of a method for performing the UE autonomous state transition from the RRC_CONNECTED state to an RRC_IDLE state as on a configured timer, according to the embodiments as disclosed herein.

In general, 3GPP is studying methods to reduce power consumption in the UE (100) and make the UE (100) more power efficient. In general, the UE (100) consumes maximum power when the UE (100) is in the RRC CONN State and the UE (100) consumes least power when the UE (100) is in one of: the RRC IDLE state and the RRC INACTIVE state. Therefore, in order to improve power efficiency the UE (100) can be moved to one of: the RRC IDLE state and the RRC INACTIVE state from the RRC CONN State when there is no data transfer expected.

Referring to the FIG. 7A, at step 702 a, the UE (100) may be in the RRC connected state and at 704 a, the UE (100) may share the UE capability exchange indicating support of the UE assisted transition to INACTIVE state. At step 706 a, the RRC Reconfiguration including the configuration to allow the UE (100) to send the indication for the transition from the RRC CONN state to the RRC INACTIVE state is conducted. Further, at step 708 a, the UE (100) may monitor the condition of one of: the timer and the counter to trigger the RRC INACTIVE state transition request. The timer may be for example the DataInactivityTimer. Further, at step 710 a, the UE (100) may determine that the condition to request the network for the state transition satisfied and at step 712 a, the UE (100) may send the indication to the wireless communication network for the state transition. Further, the in response to the indication for the state transition, the gNB (1000) of the wireless communication network may send the RRC Release message with optional resume id.

In an embodiment, the UE (100) in the RRC connected state may be allowed to send the indication for the state transition, if the UE (100) is configured with the dataInactivityTimer.

In an embodiment, if the datainactivityTimer is running, the UE (100) in the RRC Connected state may monitor a condition such as for example an inactiveIndicationThreshold condition (step 708 a) to trigger the state transition indication. On determining that the inactiveIndicationThreshold condition is met (step 710 a), the UE (100) may trigger the state transition indication to the network (step 712 a) as illustrated in the FIG. 7A. Further, the inactiveIndicationThreshold condition may be specified as a percentage or the datainactivityTimer or in terms of C-DRX cycles while the datainactivityTimer is running.

In an embodiment, the state transition indication may be a request to the network to send the UE (100) from the RRC Connected state to the RRC INACTIVE state.

In an embodiment, after triggering the state transition indication, upon expiry of the datainactivityTimer the UE (100) may move to the RRC IDLE state.

In another embodiment, the UE (100) may be allowed to send the indication for the state transition if the UE (100) is explicitly configured with the inactiveIndicationTimer.

In an embodiment, a condition to start/re-start the inactiveIndicationTimer may be same as the datainactivityTimer regardless of whether the datainactivityTimer is configured. Therefore, referring to the FIG. 7B, the UE (100) in the RRC Connected state (702 b) may trigger the state transition indication to the network (712 b), when the inactiveIndicationTimer expires (710 b), as illustrated in the FIG. 7B.

Referring to the FIG. 7C, steps 702 c to 712 c may be substantially the same and hence repeated description is omitted. At step 716 c, the RRC Release message with resume id may be not received by the UE (100). In an embodiment, after triggering the state transition indication, the UE (100) may start the waitTimer and upon expiry of the waitTimer (step 716 c), the UE (100) may move to the RRC_IDLE state as illustrated in the FIG. 7C.

In another embodiment, the UE (100) may be allowed to send the indication for the state transition, if the UE (100) is explicitly configured with inactiveIndicationTimer in addition the UE (100) is configured with dataInactivityTimer.

In an embodiment, the condition to start/re-start the inactiveIndicationTimer may be same as datainactivityTimer.

In an embodiment, if the datainactivityTimer is running, the UE (100) in the RRC Connected state may trigger the state transition indication to the network, when the inactiveIndicationTimer expires.

In an embodiment, after triggering the state transition indication, the waitTimer may starts and upon expiry of either the waitTimer or dataInactivityTimer whichever is earlier, the UE (100) may move to the RRC IDLE state.

Unlike to the conventional methods and systems, the proposed method may allow the UE (100) to inform the network about the UE capability to request or assist the serving gNB for the RRC CONN to the RRC INACTIVE state transition. On receiving the UE capability, the network may choose to one of: allow the UE (100) to request state transition when required and not allow the UE (100) to request state transition when required. If the serving gNB chooses to allow the UE (100) to request for the state transition, then the UE (100) may monitor the conditions and criteria which can eventually trigger the request to network.

In an RRC message (for example: RRCReconfiuration message), the network may provide the UE (100) with the necessary configuration required to request for the state transition. Therefore, the RRC message with the configuration required to request for the state transition may allow the UE (100) to monitor the required conditions and trigger indication to the network for the state transition from the RRC CONN to the RRC INACTIVE needed. The network may provide the configuration for one of: triggering indication to network, requesting state transition/connection release, as a timer based configuration or a counter based configuration. In current release 15 specifications, a dataInactivityTimer is used to allow the UE (100) for implicit transition to the RRC idle state.

The details of the timer handling may be as provided below:

  start or restart dataInactivityTimer:      if any MAC entity receives a MAC SDU for DTCH/ DCCH/     CCCH logical channel.      if any MAC entity transmits a MAC SDU for DTCH/ DCCH     logical channel    dataInactivityTimer Expiry:      indicate the expiry of the dataInactivityTimer to RRC    RRC handling on receiving indication of dataInactivityTimer expiry:      perform the actions upon going to RRC IDLE, with release     cause ′RRC connection failure′ MAC-CellGroupConfig ::= SEQUENCE {  drx-Config SetupRelease { DRX-Config } OPTIONAL, -- Need M  schedulingRequestConfig  SchedulingRequestConfig OPTIONAL, -- Need M  bsr-Config BSR-Config OPTIONAL, -- Need M  tag-Config TAG-Config OPTIONAL, -- Need M  phr-Config SetupRelease { PHR-Config } OPTIONAL, -- Need M  skipUplinkTxDynamic  BOOLEAN,  . . . ,  [[  csi-Mask-v1530 BOOLEAN OPTIONAL, -- Need M  dataInactivityTimer-v1530 SetupRelease { DataInactivityTimer } OPTIONAL, -- Cond MCG-Only  ]] } DataInactivityTimer ::=    ENUMERATED {s1, s2, s3, s5, s7, s10, s15, s20, s40, s50, s60, s80, s100, s120, s150, s180}

The proposed timer based configuration: The configuration may be provided conditional to the present of dataInactivityTimer.

  MAC-CellGroupConfig ::= SEQUENCE {  drx-Config SetupRelease { DRX-Config } OPTIONAL, -- Need M  schedulingRequestConfig  SchedulingRequestConfig OPTIONAL, -- Need M  bsr-Config BSR-Config OPTIONAL, -- Need M  tag-Config TAG-Config OPTIONAL, -- Need M  phr-Config SetupRelease { PHR-Config } OPTIONAL, -- Need M  skipUplinkTxDynamic  BOOLEAN,  . . . ,  [[  csi-Mask-v1530   BOOLEAN OPTIONAL, -- Need M  dataInactivityTimer-v1530    SetupRelease { DataInactivityTimer } OPTIONAL, -- Cond MCG-Only  ]]   [[  inactiveIndicationTimer-r16     SetupRelease { InactiveIndicationTimer }  OPTIONAL, -- Cond DataInactTimer   ]] } DataInactivityTimer ::=       ENUMERATED {s1, s2, s3, s5, s7, s10, s15, s20, s40, s50, s60, s80, s100, s120, s150, s180} InactiveIndicationTimer-r16 ENUMERATED {0dot2, 0dot4, 0dot6, 0dot8}

The MAC-CellGroupConfig field descriptions are provided in table. 1 and the conditional presence is described in table. 2.

TABLE 1 MAC-CellGroupConfig field descriptions csi-Mask-v1530 If set to true, the UE limits CSI reports to the on-duration period of the DRX cycle, see TS 38.321 [3]. dataInactivityTimer-v1530 Releases the RRC connection upon data inactivity as specified in clause 5.3.8.5 and in TS 38.321 [3]. Value s1 corresponds to 1 second, s2 corresponds to 2 seconds and so on. drx-Config Used to configure DRX as specified in TS 38.321 [3]. inactiveIndicationTimer-r16 Triggers UL transmission to indicate the network about need to transition to INACTIVE state due to data inactivity. Value 0dot2 refers to 20% of dataInactivityTimer and so on. skip UplinkTxDynamic If set to true, the UE skips UL transmissions for an uplink grant other than a configured uplink grant if no data is available for transmission in the UE buffer as described in TS 38.321 [3]. FFS: configurable per SCell?

TABLE 2 Conditional Presence Explanation MCG-Only This field is optionally present, Need M, for the MAC- CellGroupConfig of the MCG. It is absent otherwise. DataInactTimer The field is optionally present, Need M, for MAC entity when dataInactivityTimer is configured. It is absent otherwise.

Handling of inactiveIndicationTimer: The MAC may handle this timer based on data activity on the MAC entity and indicate to RRC once the configured threshold timer condition is satisfied.

5.19 Data Inactivity Monitoring (38.321)

The UE may be configured by RRC with a Data inactivity monitoring functionality, when in RRC_CONNECTED. RRC controls Data inactivity operation by configuring the timer dataInactivityTimer.

When dataInactivityTimer is configured, the UE shall:

1> if inactiveIndicationTimer is not configured;

-   -   2> if any MAC entity receives a MAC SDU for DTCH logical         channel, DCCH logical channel, or CCCH logical channel; or     -   2> if any MAC entity transmits a MAC SDU for DTCH logical         channel, or DCCH logical channel:         -   3> start or restart dataInactivityTimer.     -   2> if the dataInactivityTimer expires:         -   3> indicate the expiry of the dataInactivityTimer to upper             layers.             1> else, if inactiveIndicationTimer is configured;     -   2> if any MAC entity receives a MAC SDU for DTCH logical         channel, DCCH logical channel, or CCCH logical channel; or     -   2> if any MAC entity transmits a MAC SDU for DTCH logical         channel, or DCCH logical channel:         -   3> start or restart inactiveIndicationTimer.     -   2> if the inactiveIndicationTimer expires:         -   3> indicate the expiry of the inactiveIndicationTimer to             upper layers.             5.3.8.6 UE Actions Upon the Expiry of             inactiveIndicationTimer (38.331)             Upon receiving the expiry of inactiveIndicationTimer from             lower layers while in RRC_CONNECTED, the UE shall:             1> initiate transmission of UEAssistanceMessage with             inactiveIndication set.

Alternatively, the network may configure the UE with inactiveIndicationTimer independent of dataInactivityTimer. In such cases, the handling is as illustrated below:

Configuration: MAC-CellGroupConfig ::= SEQUENCE {  drx-Config SetupRelease { DRX-Config } OPTIONAL, -- Need M  schedulingRequestConfig  SchedulingRequestConfig OPTIONAL, -- Need M  bsr-Config BSR-Config OPTIONAL, -- Need M  tag-Config TAG-Config OPTIONAL, -- Need M  phr-Config SetupRelease { PHR-Config } OPTIONAL, -- Need M  skipUplinkTxDynamic  BOOLEAN,  . . . ,  [[  csi-Mask-v1530   BOOLEAN OPTIONAL, -- Need M  dataInactivityTimer-v1530   SetupRelease { DataInactivityTimer } OPTIONAL, -- Cond MCG-Only  ]]   [[  inactiveIndicationTimer-r16    SetupRelease { InactiveIndicationTimer }  OPTIONAL, -- Need M   ]] } DataInactivityTimer ::=     ENUMERATED {s1, s2, s3, s5, s7, s10, s15, s20, s40, s50, s60, s80, s100, s120, s150, s180} InactiveIndicationTimer-r16 ENUMERATED {ms200, ms500, ms1000, ms2000, ms5000, ms10000}

Further, the MAC-CellGroupConfig field descriptions is provided in the table. 3.

TABLE 3 MAC-CellGroupConfig field descriptions csi-Mask-v1530 If set to true, the UE limits CSI reports to the on-duration period of the DRX cycle, see TS 38.321 [3]. dataInactivityTimer-v1530 Releases the RRC connection upon data inactivity as specified in clause 5.3.8.5 and in TS 38.321 [3]. Value s1 corresponds to 1 second, s2 corresponds to 2 seconds and so on. drx-Config Used to configure DRX as specified in TS 38.321 [3]. inactiveIndicationTimer-r16 Triggers UL transmission to indicate the network about need to transition to INACTIVE state due to data inactivity. Value ms 200 refers to 200 ms and so on. skip UplinkTxDynamic If set to true, the UE skips UL transmissions for an uplink grant other than a configured uplink grant if no data is available for transmission in the UE buffer as described in TS 38.321 [3]. FFS: configurable per SCell?

Handling of inactiveIndicationTimer: The MAC may handle this timer based on data activity on the MAC entity and indicate to RRC once the configured threshold timer condition is satisfied.

5.19 Data Inactivity Monitoring (38.321)

The UE may be configured by RRC with a Data inactivity monitoring functionality, when in RRC_CONNECTED. RRC controls Data inactivity operation by configuring the timer dataInactivityTimer.

When dataInactivityTimer is configured, the UE shall:

1> if any MAC entity receives a MAC SDU for DTCH logical channel, DCCH logical channel, or CCCH logical channel; or

1> if any MAC entity transmits a MAC SDU for DTCH logical channel, or DCCH logical channel:

-   -   2> start or restart dataInactivityTimer.         1> if the dataInactivityTimer expires:     -   2> indicate the expiry of the dataInactivityTimer to upper         layers.         5.X Inactivity Indication Monitoring (38.321)         When dataInactivityTimer is configured, the UE shall:         1> if any MAC entity receives a MAC SDU for DTCH logical         channel, DCCH logical channel, or CCCH logical channel; or         1> if any MAC entity transmits a MAC SDU for DTCH logical         channel, or DCCH logical channel:     -   2> start or restart inactiveIndicationTimer.         1> if the inactiveIndicationTimer expires:     -   2> indicate the expiry of the inactiveIndicationTimer to upper         layers.         5.3.8.6 UE Actions Upon the Expiry of inactiveIndicationTimer         (38.331)         Upon receiving the expiry of inactiveIndicationTimer from lower         layers while in RRC_CONNECTED, the UE shall:         1> initiate transmission of UEAssistanceMessage with         inactiveIndication set.

The proposed counter based configuration: The need for transition to INACTIVE state can be monitored based on a count of DRX cycles without data inactivity. If the configured number of DRX cycles have elapsed without any transmission or reception (drxInactivityTimer is not started even once during this duration), the UE (100) initiates transmission of stat transition indication to network.

DRX-Config ::= SEQUENCE {  drx-onDurationTimer  CHOICE {   subMilliSeconds INTEGER (1 . . . 31),   milliSeconds ENUMERATED {    ms1, ms2, ms3, ms4, ms5, ms6, ms8, ms10, ms20, ms30, ms40, ms50, ms60,    ms80, ms100, ms200, ms300, ms400, ms500, ms600, ms800, ms1000, ms1200,    ms1600, spare8, spare7, spare6, spare5, spare4, spare3, spare2, sparel }   },  drx-InactivityTimer  ENUMERATED {   ms0, ms1, ms2, ms3, ms4, ms5, ms6, ms8, ms10, ms20, ms30, ms40, ms50, ms60, ms80,   ms100, ms200, ms300, ms500, ms750, ms1280, ms1920, ms2560, spare9, spare8,   spare7, spare6, spare5, spare4, spare3, spare2, spare1 },  drx-HARQ-RTT-TimerDL    INTEGER (0 . . . 56),  drx-HARQ-RTT-TimerUL    INTEGER (0 . . . 56),  drx-RetransmissionTimerDL  ENUMERATED {  sl0, sl1, sl2, sl4, sl6, sl8, sl16, sl24, sl33, sl40, sl64, sl80, sl96, sl112, sl128,  sl160, sl320, spare15, spare14, spare13, spare12, spare11, spare10, spare9,  spare8, spare7, spare6, spare5, spare4, spare3, spare2, spare1 },  drx-RetransmissionTimerUL  ENUMERATED {  sl0, sl1, sl2, sl4, sl6, sl8, sl16, sl24, sl33, sl40, sl64, sl80, sl96, sl112, sl128,  sl160, sl320, spare15, spare14, spare13, spare12, spare11, spare10, spare9,  spare8, spare7, spare6, spare5, spare4, spare3, spare2, spare1 },  drx-LongCycleStartOffset CHOICE {   ms10   INTEGER(0 . . . 9),   ms20   INTEGER(0 . . . 19),   ms32   INTEGER(0 . . . 31),   ms40   INTEGER(0 . . . 39),   ms60   INTEGER(0 . . . 59),   ms64   INTEGER(0 . . . 63),   ms70   INTEGER(0 . . . 69),   ms80   INTEGER(0 . . . 79),   ms128   INTEGER(0 . . . 127),   ms160   INTEGER(0 . . . 159),   ms256   INTEGER(0 . . . 255),   ms320   INTEGER(0 . . . 319),   ms512   INTEGER(0 . . . 511),   ms640   INTEGER(0 . . . 639),   ms1024   INTEGER(0 . . . 1023),   ms1280   INTEGER(0 . . . 1279),   ms2048   INTEGER(0 . . . 2047),   ms2560   INTEGER(0 . . . 2559),   ms5120   INTEGER(0 . . . 5119),   ms10240   INTEGER(0 . . . 10239) },  shortDRX SEQUENCE {   drx-ShortCycle   ENUMERATED {    ms2, ms3, ms4, ms5, ms6, ms7, ms8, ms10, ms14, ms16, ms20, ms30, ms32,      ms35, ms40, ms64, ms80, ms128, ms160, ms256, ms320, ms512, ms640, spare9,      spare8, spare7, spare6, spare5, spare4, spare3, spare2, spare1 },     drx-ShortCycleTimer   INTEGER (1 . . . 16)  } OPTIONAL, -- Need R  drx-SlotOffset INTEGER (0 . . . 31)   [[   inactiveIndciationCounter-r16  SetupRelease { InactiveIndciationCounter }   ]] } InactiveIndciationCounter ENUMERATED {n2, n5, n10, n25, n100}

Further, the DRX-Config field descriptions is provided in the table. 4.

TABLE 4 DRX-Config field descriptions drx-HARQ-RTT-TimerDL Value in number of symbols of the BWP where the transport block was received. drx-HARQ-RTT-TimerUL Value in number of symbols of the BWP where the transport block was transmitted. drx-InactivityTimer Value in multiple integers of 1 ms. ms 0 corresponds to 0, ms 1 corresponds to 1 ms, ms 2 corresponds to 2 ms, and so on. drx-LongCycleStart Offset drx-LongCycle in ms and drx-StartOffset in multiples of 1 ms. If drx- ShortCycle is configured, the value of drx-LongCycle shall be a multiple of the drx-ShortCycle value. drx-onDurationTimer Value in multiples of 1/32 ms (subMilliSeconds) or in ms (milliSecond). For the latter, ms 1 corresponds to 1 ms, ms 2 corresponds to 2 ms, and so on. drx-RetransmissionTimerDL Value in number of slot lengths of the BWP where the transport block was received. s10 corresponds to 0 slots, s11 corresponds to 1 slot, s12 corresponds to 2 slots, and so on. drx-RetransmissionTimerUL Value in number of slot lengths of the BWP where the transport block was transmitted. s10 corresponds to 0 slots, s11 corresponds to 1 slot, s12 corresponds to 2 slots, and so on. drx-ShortCycleTimer Value in multiples of drx-ShortCycle. A value of 1 corresponds to drx- ShortCycle, a value of 2 corresponds to 2 * drx-ShortCycle and so on. drx-ShortCycle Value in ms. ms 1 corresponds to 1 ms, ms 2 corresponds to 2 ms, and so on. drx-SlotOffset Value in 1/32 ms. Value 0 corresponds to 0 ms, value 1 corresponds to 1/32 ms, value 2 corresponds to 2/32 ms, and so on. inactiveIndciationCounter Triggers UL transmission to indicate the network about need to transition to INACTIVE state due to data inactivity. Value n2 refers to 2 drx cycles and so on. 5.3.8.x UE Actions Upon Satisfying inactiveIndicationCounter (38.331) Upon satisfying the condition of not having and DL reception or UL transmission for inactiveIndicationCounter count of DRX, from lower layers while in RRC_CONNECTED, the UE shall: 1> initiate transmission of UEAssistanceMessage with inactiveIndication set.

Table. 5 illustrates throughput measurements for NR calculated at the Radio link control (RLC) layer based on data volume between reference time points at the RLC layer. The method to perform Layer 2 throughput measurements by gNB/NG-eNB is described. Performance measurements for 5G networks including throughput measurements at gNB are defined in the SA5 TS 28.552 “5G performance measurements”. RAN2 also studied the feasibility of SA5 defined measurements related to RAN2. Generally, the throughput measurements are calculated at PDCP SDU level based on data volume between reference time points at PDCP layer in LTE. However, the throughout measurements for NR are calculated at RLC layer based on data volume between reference time points at RLC layer as illustrated in table.5.

TABLE 5 LTE: Scheduled IP Throughput in DL (Similar measurement defined for as well) The measurement is performed per QCI per UE. ${{{If}\mspace{14mu}{\sum{ThpTimeDl}}} > 0},{\frac{\sum{ThpVolDl}}{\sum{ThpTimeDl}} \times {1000\;\left\lbrack {{kbits}\text{/}s} \right\rbrack}}$ If  ∑ThpTimeDl = 0, 0 [kbits/s] For small data bursts, where all buffered data is included in one initial HARQ transmission, ThpTimeDl = 0, otherwise ThpTimeDl = T1 − T2 [ms] ThpTimeDl The time to transmit a data burst excluding the last piece of data transmitted in the TTI when the buffer is emptied. A sample of “ThpTimeDl” for each time the DL buffer for one E-RAB is emptied. T1 The point in time after T2 when data up until the second last piece of data in the transmitted data burst which emptied the PDCP SDU available for transmission for the particular E-RAB was successfully transmitted, as acknowledged by the UE. T2 The point in time when the first transmission begins after a PDCP SDU becomes available for transmission, where previously no PDCP SDUs were available for transmission for the particular E-RAB. ThpVolDl The volume of a data burst, excluding the data transmitted in the TTI when the buffer is emptied. A sample for ThpVolDl is the data volume, counted on PDCP SDU level, in kbits successfully transmitted (acknowledged by UE) in DL for one E-RAB during a sample of ThpTimeDl. It shall exclude the volume of the last piece of data emptying the buffer. NR: Average DL UE throughput in gNB (Similar measurement defined for as well) The measurement is optionally split into subcounters per QoS level ${{{If}\mspace{14mu}{\sum\limits_{UEs}{\sum{ThpTimeDl}}}} > 0},{\frac{\sum\limits_{UEs}{\sum{ThpVolDl}}}{\sum\limits_{UEs}{\sum{ThpTimeDl}}} \times {1000\;\left\lbrack {{kbits}\text{/}s} \right\rbrack}}$ ${{{If}\mspace{14mu}{\sum\limits_{UEs}{\sum{ThpTimeDl}}}} = 0},{0\;\left\lbrack {{kbits}\text{/}s} \right\rbrack}$ For small data bursts, where all buffered data is included in one initial HARQ transmission, ThpTimeDl = 0, otherwise ThpTimeDl = T1 − T2 [ms] ThpTimeDl The time to transmit a data burst excluding the data transmitted in the slot when the buffer is emptied. A sample of “ThpTimeDl” for each time the DL buffer for one DataRadioBearer (DRB) is emptied. T1 The point in time after T2 when data up until the second last piece of data in the transmitted data burst which emptied the RLC SDU available for transmission for the particular DRB was successfully transmitted, as acknowledged by the UE. T2 The point in time when the first transmission begins after a RLC SDU becomes available for transmission, where previously no RLC SDUs were available for transmission for the particular DRB. ThpVolDl The RLC level volume of a data burst, excluding the data transmitted in the slot when the buffer is emptied. A sample for ThpVolDl is the data volume, counted on RLC SDU level, in kbits successfully transmitted (acknowledged by UE) in DL for one DRB during a sample of ThpTimeDl. (It shall exclude the volume of the last piece of data emptying the buffer).

Further, the throughput measurements defined for NR by SA5 may be performed at RLC layer whereas in LTE, it is measured at PDCP layer.

A QoS flow may be the smallest granularity over which QoS verification can be performed by the network. The mapping between QoS flow and DRB in NR is not always one to one and can also be many to one. Therefore, performing throughput measurement at RLC layer alone is not sufficient to verify QoS and identify the throughput per QoS flow. An analysis of adequacy of RLC level throughput measurements for different possible bearer configuration on NR is illustrated below:

TABLE 6 Bearer termination point (RAN RLC layer Bearer node with Connected measurement No Type PDCP) CN Sufficient? Remarks 1 Direct gNB 5GC NO RB may bearer on have NR multiple QoS flows mapped to it. 2 gNB EPC YES PDCP Throughput = RLC Throughput 3 Split gNB 5GC NO RB may 4 bearer on eNB 5GC NO have NR multiple QoS flows mapped to it. 5 gNB EPC YES 6 eNB EPC YES PDCP Throughput = Sum of both RLC entity throughputs

All the bearer types configured on the NR can estimate the QoS correctly if the throughput measurement is done only based on the RLC data volume at the RLC layer.

In the NR a PDU session can include multiple QoS flows and SDAP entity can map one or more QoS flows onto a single DRB. The restriction in the QoS flow to DRB mapping is that one QoS flow is mapped onto only one DRB at a time. For radio bearers on the NR which is connected to 5GC, the QoS termination point on gNB is SDAP entity. Therefore, in order to verify QoS over an IP flow for bearers connected to 5GC, the throughput has to be measured at SDAP layer. For radio bearer on NR which is connected to EPC, the QoS termination point on eNB is PDCP entity. In order to verify QoS for an IP flow for bearers connected to EPC, the throughput has to be measured at PDCP entity. The method proposes that for the NR and the LTE bearers connected to 5GC, the throughput measurement has to be done based on the SDAP SDU at the SDAP layer. The method proposes that for the NR and the LTE bearers connected to EPC, the throughput measurement has to be done based on the PDCP SDU at the PDCP layer.

In case of split bearers, the PDCP throughput may not always be reflected as the sum of throughputs of the RLC entities it is connected to. For radio bearers for which PDCP duplication is configured, the throughput measurement has to be performed based on PDCP SDU volume. The method proposes that for the radio bearers configured with the PDCP duplication, the throughput measurement has to be done based on the PDCP SDU at the PDCP layer.

In MR-DC cases, there are split bearers that can be configured with termination point on gNB/NR and the split leg on eNB/LTE. In such cases, in order to measure throughput over the DRB, the gNB has to consider the throughput provided over both the legs. Therefore, the gNB would add the throughput on NR RLC entity and LTE RLC entity. However, there is no throughput measurement performed on LTE RLC as per current release 15 specification. Provision to measure throughput based on RLC SDU on LTE, for split bearers terminating on gNB, has to be introduced. It is proposed that introduce throughput measurement based on RLC SDU at RLC layer on eNB, when split bearer with termination on gNB is configured to the UE (100).

FIG. 8 illustrates a gNB according to the embodiments as disclosed herein.

The gNBs, eNBs or BSs described above may correspond to the gNB 800. For example, the source gNB (1000 a) and/or the target gNB (1000 b) illustrated in FIG. 1A may correspond to the gNB 800.

Referring to the FIG. 8, the gNB 800 may include a processor 830, a transceiver 810 and a memory 820. However, all of the illustrated components are not essential. The gNB 800 may be implemented by more or less components than those illustrated in FIG. 8. In addition, the processor 830 and the transceiver 810 and the memory 820 may be implemented as a single chip according to another embodiment.

The aforementioned components will now be described in detail.

The processor 830 may include one or more processors or other processing devices that control the proposed function, process, and/or method. Operation of the gNB 800 may be implemented by the processor 830.

The processor 830 may control the transceiver 810 to transmit a radio resource control (RRC) reconfiguration message to UE when the UE is in an RRC connected state. The RRC reconfiguration message may include a handover configuration.

The transceiver 810 may include a RF transmitter for up-converting and amplifying a transmitted signal, and a RF receiver for down-converting a frequency of a received signal. However, according to another embodiment, the transceiver 810 may be implemented by more or less components than those illustrated in components.

The transceiver 810 may be connected to the processor 830 and transmit and/or receive a signal. The signal may include control information and data. In addition, the transceiver 810 may receive the signal through a wireless channel and output the signal to the processor 830. The transceiver 810 may transmit a signal output from the processor 830 through the wireless channel.

The memory 820 may store the control information or the data included in a signal obtained by the gNB 800. The memory 820 may be connected to the processor 830 and store at least one instruction or a protocol or a parameter for the proposed function, process, and/or method. The memory 830 may include read-only memory (ROM) and/or random access memory (RAM) and/or hard disk and/or CD-ROM and/or DVD and/or other storage devices.

FIG. 9 illustrates a user equipment (UE) according to the embodiments as disclosed herein.

The UEs described above may correspond to the UE 900. For example, the UE 100 illustrated in FIG. 1A and FIG. 1B may correspond to the UE 900.

Referring to the FIG. 9, the UE 900 may include a processor 930, a transceiver 910 and a memory 920. However, all of the illustrated components are not essential. The UE 900 may be implemented by more or less components than those illustrated in FIG. 9. In addition, the processor 930 and the transceiver 910 and the memory 920 may be implemented as a single chip according to another embodiment.

The aforementioned components will now be described in detail.

The processor 930 may include one or more processors or other processing devices that control the proposed function, process, and/or method. Operation of the UE 900 may be implemented by the processor 930.

The processor 930 may control the transceiver 910 to receive a radio resource control (RRC) reconfiguration message from a source cell of the wireless communication network, wherein the UE is in an RRC connected state and wherein the RRC reconfiguration message comprises a handover configuration. In addition, the processor 930 may determine whether a CHO configuration is provided in the handover configuration, wherein the CHO configuration comprises a plurality of conditions for executing the CHO and a plurality of target cell configurations. The processor 930 may perform one of: continuing a Radio Link Monitoring (RLM) timer and a radio link monitoring procedure on the source cell, in response to determining that the CHO configuration is provided in the handover configuration, and stopping the RLM timer and suspending the radio link monitoring procedure on the source cell, in response to determining that the CHO configuration is not provided in the handover configuration. The processor 930 may execute the CHO from the source cell to a candidate target cell of the plurality of target cells in the wireless communication network based on the CHO configuration.

The transceiver 910 may include a RF transmitter for up-converting and amplifying a transmitted signal, and a RF receiver for down-converting a frequency of a received signal. However, according to another embodiment, the transceiver 910 may be implemented by more or less components than those illustrated in components.

The transceiver 910 may be connected to the processor 930 and transmit and/or receive a signal. The signal may include control information and data. In addition, the transceiver 910 may receive the signal through a wireless channel and output the signal to the processor 930. The transceiver 910 may transmit a signal output from the processor 930 through the wireless channel.

The memory 920 may store the control information or the data included in a signal obtained by the UE 900. The memory 920 may be connected to the processor 920 and store at least one instruction or a protocol or a parameter for the proposed function, process, and/or method. The memory 3330 may include read-only memory (ROM) and/or random access memory (RAM) and/or hard disk and/or CD-ROM and/or DVD and/or other storage devices.

The embodiments disclosed herein can be implemented through at least one software program running on at least one hardware device and performing network management functions to control the elements.

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Although the present disclosure has been described with various embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims. 

What is claimed is:
 1. A method for executing conditional handover (CHO) by a User Equipment (UE) in a wireless communication network, comprising: receiving, from a source cell, a radio resource control (RRC) reconfiguration message including first conditional handover (CHO) configuration information; identifying one or more execution conditions for performing CHO and a plurality of target cell configurations included in the first CHO configuration information; continuing a Radio Link Monitoring (RLM) timer and an RLM procedure on the source cell until a first candidate target cell from a plurality of candidate target cells satisfies at least one execution condition from the one or more execution conditions for performing the CHO; and when the first candidate target cell satisfies at least one execution condition from the one or more execution conditions for performing the CHO, executing the CHO from the source cell to the first candidate target cell and stopping the RLM timer based on a first candidate target cell configuration corresponding to the first candidate target cell from the plurality of target cell configurations included in the first CHO configuration information.
 2. The method as claimed in claim 1, further comprising: receiving, from the source cell, a handover command without second CHO configuration information before the first candidate target cell satisfies the at least one execution condition from the one or more execution conditions; suspending the RLM timer and the RLM procedure on the source cell regardless of the first CHO configuration information; and executing a handover procedure from the source cell to a second target cell.
 3. The method as claimed in claim 1, wherein the first CHO configuration comprises a condition for executing the CHO for the first candidate target cell.
 4. The method as claimed in claim 1, wherein the plurality of target cell configurations are carried in the RRC reconfiguration message as an OCTET string.
 5. The method as claimed in claim 1, wherein the first CHO configuration is a delta configuration to a current source cell configuration.
 6. The method as claimed in claim 1, wherein the plurality of target cell configurations are generated by the plurality of candidate target cells.
 7. The method as claimed in claim 1, wherein the one or more execution conditions for performing CHO are generated by the source cell.
 8. The method as claimed in claim 1, wherein the RLM timer is a T310 timer.
 9. A User Equipment (UE) for executing conditional handover (CHO) in a wireless communication network, the UE comprising: a memory; a transceiver coupled to the memory; and at least one processor coupled to the memory and the transceiver, the at least one processor configured to: control the transceiver to receive, from a source cell, a radio resource control (RRC) reconfiguration message including first conditional handover (CHO) configuration information; identify one or more execution conditions for performing CHO and a plurality of target cell configurations included in the first CHO configuration information; continue a Radio Link Monitoring (RLM) timer and a radio link monitoring procedure on the source cell until a first candidate target cell from a plurality of candidate target cells satisfies at least one execution condition from the one or more execution conditions for performing the CHO; and when the first candidate target cell satisfies at least one execution condition from the one or more execution conditions for performing the CHO, execute the CHO from the source cell to the first candidate target cell and stop the RLM timer based on a first candidate target cell configuration corresponding to the first candidate target cell from the plurality of target cell configurations included in the first CHO configuration information.
 10. The UE as claimed in claim 9, wherein the at least one processor is further configured to: receive, from the source cell, a handover command without second CHO configuration information before the first candidate target cell satisfies the at least one execution condition from the one or more execution conditions; suspend the RLM timer and the radio link monitoring procedure on the source cell regardless of the first CHO configuration information; and execute a handover procedure from the source cell to a second target cell.
 11. The UE as claimed in claim 9, wherein the first CHO configuration comprises a condition for executing the CHO for the first candidate target cell and the first candidate target cell configuration.
 12. The UE as claimed in claim 9, wherein the plurality of target cell configurations is carried in the RRC reconfiguration message as an OCTET string.
 13. The UE as claimed in claim 9, wherein the first CHO configuration is a delta configuration to a current source cell configuration.
 14. The UE as claimed in claim 9, wherein the plurality of target cell configurations are generated by the plurality of candidate target cells.
 15. The UE as claimed in claim 9, wherein the one or more execution conditions for performing CHO are generated by the source cell.
 16. The UE as claimed in claim 9, wherein the RLM timer is a T310 timer.
 17. A method for executing conditional handover (CHO) by a source cell in a wireless communication network, comprising: transmitting, to a user equipment (UE), a radio resource control (RRC) reconfiguration message including first conditional handover (CHO) configuration information including one or more execution conditions for performing CHO and a plurality of target cell configurations; identifying that a Radio Link Monitoring (RLM) procedure on the source cell is continued until a first candidate target cell from a plurality of candidate target cells satisfies at least one execution condition from the one or more execution conditions for performing the CHO; and identifying that the RLM procedure on the source cell is suspended when the first candidate target cell satisfies at least one execution condition from the one or more execution conditions for performing the CHO.
 18. The method as claimed in claim 17, further comprising: transmitting, to the UE, handover command without second CHO configuration information before the first candidate target cell satisfies the at least one execution condition from the one or more execution conditions; and identifying that the RLM procedure on the source cell is suspended regardless of the first CHO configuration information.
 19. The method as claimed in claim 17, wherein the plurality of target cell configurations is carried in the RRC reconfiguration message as an OCTET string.
 20. The method as claimed in claim 17, wherein the plurality of target cell configurations is generated by the plurality of candidate target cells, and wherein the one or more execution conditions for performing CHO are generated by the source cell. 